Remedies: Do’s for Welding Austenitic Stainless Steel
Stainless steel is the type of high alloy steel with at least 11.5% Chromium. Iron content exceeds that of any other element. Carbon is generally less than 1.5%.
Properties of Stainless Steel:
Mechanical Properties: Compared to other materials, stainless steel has strong mechanical properties at ambient temperatures, In particular, it combines ductility, elasticity, and hardness, In addition, it offers good mechanical behavior at both low and high temperatures. So widely used in all Industries.
Oxidation Resistance: Stainless steel has the best resistance of all metallic materials when used in structural applications, having a critical temperature above 800°C. Grades of Stainless steel can be used for Sub-zero temperatures.
Corrosion Resistance: With a minimum chromium content of 10.5%, stainless steel is continuously protected by a passive chromium oxide layer, This special feature gives stainless steel its resistance to corrosion.
Versatility: Stainless steel has a wide variety of finishes, from matte to bright, including brushed and engraved. It is widely used by architects for building envelopes, interior design, and street furniture.
Easy Maintenance: Stainless steel objects are easy to clean, and common cleaning agents.
Environment friendly: Stainless steel is the “green material” and is infinitely recyclable. It is environmentally neutral and inert when in contact with elements like water, and it does not release compounds that could change their composition.
Types of Stainless Steel Used in Industry:
AusteniticNon-Magnetic & work Hardening
Ferritic Soft & Magnetic
MartensiticMagnetic & Hard
Duplex Magnetic & Wok Hardening
Precipitation Hardening
Problems in Welding Austenitic SS:
Carbide Precipitation or IGC
Heat of Welding
Porosity
Contamination
Carbide Precipitation or Inter Granular Corrosion:
The major problem encountered in welding austenitic stainless steel is intergranular corrosion or carbide precipitation.
When welding Austenitic SSbetween 420 to 880 deg. C base metal temperature also known as “Sensitisation Temperature”a large volume of Cr is pickedin the grain Boundaries of the HAZ area
This forms Chromium Carbide which precipitates and forms at grain boundaries –the area adjacent to the HAZ area
So on working condition or in service, the HAZ area starts corroding at a faster rate as this area cannot form Cr2O3 due to Cr depletion
This phenomenon is called Inter Granular Corrosion or Carbide Precipitation
Remedies:
Controlling the carbon content (0.03% or below)
Addition of Carbide stabilizers like Ti, Nb.
Heat Treatment (Solution annealing).
Controlled welding below 450 Degrees
The heat of welding:
Cracking from the HAZ area
Loss of Corrosion Resistance
Warping or Distortion of Material
Loss of Mechanical Properties
Porosity :
This is caused by Dirt, Grease & marking material
Poor Quality of Flux coating
Contamination:
Contaminants in SS like Sulphur, Carbon, Iron, Copper & lead is the root Couse of failure of welded joints and also poor corrosion resistance
Remedies: Do’s for Welding Austenitic Stainless Steel:
Rigid Fixturing with more tack welds
Sequence welding to control heat
Baking of electrode 200 deg –one hour before welding.
Proper Cleaning of weld area before starting the job
Use short arc & low heat Input Welding Electrodes
Use Correct or optimum diameter electrode during welding
We at Ador Fontech have designed & developed this exclusive range of LH- Low heat Input Welding Electrodes, TIG & MIG wires for welding of all types of stainless including austenitic stainless steels.
Cast iron can be described as a wide variety of iron-based materials containing Carbon of 1.7%-4.5%
It also contains Silicon- 0.5%-3%, Manganese-0.2%-1.3%, Phosphorous-0.8% max & Sulphur -0.2%max. The major distinguishing feature between steels is carbon content, it has maximum influence on the property of CI. A low percentage promotes the formation of hard white cast iron & higher percentage promotes the formation of grey cast iron.
Properties of Cast Iron:
Hardness: Cast iron is hard and it can be hardened by heating and sudden cooling. This makes it quite durable.
Melting Point: Cast iron has a lower melting point (1200 deg. C) as compared to the melting point of mild steel which lies in the range of 1300 deg. C and 1400 deg. C.
Castability: Cast iron is easier to cast when it comes to casting shapes out of the material. Due to the extra carbon & silicon present in cast iron, its molten form is more fluid and this makes it easier to cast the material into complex shapes.
Machinability: Cast iron is almost elastic up to ultimate tensile strength and produces discontinuous chips which break away from the sample easily. This helps to improve the cutting ability. Due to this, cast iron is the preferred material when it comes to high machinability and strength.
Highly porous hence it can be used in machine bases etc. as it provides good self-lubrication properties as oil & grease remain in the porous mass of cast iron.
It’s Porous and sponge-like structure means it can be used in machine bases as it has good damping properties
Types of Cast Iron Used in Industry:
Grey Cast Iron
White Cast Iron
Chilled Cast Iron
Nodular Cast Iron
Malleable Cast Iron
Alloyed Cast Iron
Depending on carbon content and the procedure it is manufactured and these are common grades used in industry.
Problems in Welding Cast Iron:
CI is Brittle, so it tends to crack easily
Porous & Contaminated so cleaning is very tough
Too much Carbon tends to crack during welding
Lesser Heat Conductivity, so heat dissipation is fast
Carbon Pick up in the weld metal will be there leading to cracks in the HAZ.
Techniques to Weld Cast Iron.
Considering the above problems in cast iron, there are two methods or techniques to weld cast iron.
Hot Technique
Cold Technique
Hot Technique:
Preheat the cast iron component to 350 deg. C – 400 deg. C
Do the welding at the same temperature, ensure the temperature is maintained above 350 deg. C during the entire process of welding
Slow cool the welded component by gradually cooling the component, if the job was done with heating cold reduce 50 deg. C per hour for per inch thickness of the job, If done in a furnace switch off & allow it to cool.
Cold Technique
Limit heat input in the cast iron weldingjob by adopting the following methods :
Low current: Use low heat input welding electrodes & use lower diameter and lower amperages.
Stringer bead: Strictly no weaving during welding use only stringer beads
Short arc: Use arc length less than the diameter of electrode, preferable touch & weld type LH products
Short bead length: Weld not more than 25 -30mm bead length only, always weld with a job on hand heat
Peening: Hot peening with the ball-peen hammer is recommended for removing any residual stress in welding.
For welding of all weld-able grade cast iron, Nickel-based electrodes either pure nickel or Ferro-nickel type electrodes are used depending on the application requirements.
We at Ador Fontech have designed & developed this exclusive Range of LH Low heat Input Welding Electrodes for welding cast iron using both welding techniques required for cast iron welding
One of our most important manufactured products used in all industries has many applications & uses. Steel can be molded, pressed, machined, welded & woven to suit different purposes.
Steel making: It’s a three-step process.
Iron Making: Iron ore, coke & a flux (limestone) are combined in a blast furnace to produce molten iron containing about 4% carbon.
Steel Making: Excess carbon is removed in a basic oxygen steel making vessel and the required alloy is added. The molten steel is then cast into billets, blooms, or slabs.
Shaping: Steel is rolled to various sizes and shapes in a rolling mill.
Steels are basically a wide range of iron-based alloys with carbon up to 1 .7 %.
In plain carbon steels other elements are silicon (up to 0.6%), manganese(up to 1.65%), sulphur (up to 0.35%) & phosphorous (up to 0.13%).
1. Elements in Steel:
Carbon
Up to 1.7 %
Promotes formation of carbides (cementite, pearlite & martensite)
Manganese
Deoxidizes the metal and facilitates hot working
Neutralizes sulfur by forming manganese sulfide which increases strength
Provides work-hardening property
Silicon
Deoxidizes steel
Increases resistance to scaling
Phosphorous
An impurity
Decreases ductility and toughness
Sulfur
An impurity
Decreases strength and impact resistance
Improves machinability
2. Types of Steel :
Low Carbon Steels
Carbon up to 0.3 %
Good ductility & weldability
Comparatively low strength & not easily heat treatable
Welding: Have very good weldability.
No special precautions required
Medium Carbon steels
Carbon 0.3 to 0.6 %
Better strength & hardness than low carbon steel
Welding: Slight preheat around 200-250 deg. C and slow cooling.
Use a low hydrogen type electrode
High Carbon Steels
Carbon : 0.6 % to 1.71 %
Easily heat treatable to high hardness
Welding: Poor weldability.
Tendency to crack
High preheat around 300 deg. C and very slow cooling
Maintain high interpass temperature-300 deg. C
Post weld heat treatment and stresses relieving desirable
Alloy Steels
Contain alloying elements other than silicon, manganese, sulfur & phosphorous
High Alloy Steels
Alloying elements more than 10 % ( Ni, Mn, Cr)
Welding: High carbon equivalent hence form martensite.
Preheat around 300 deg. C and maintain interpass
Cool slowly
Low Alloy Steels
Alloying elements less than 10 %
Welding:Preheat requirements minimum.
Types of High Alloy Steels :
Austenitic Manganese steels:
More than 10 % manganese & high carbon
Known as Hadfield Steels
Work harden in service
Welding: Forms hard Carbides at temperatures above 175 deg. C.
No, preheat and fast cooling
Stainless Steels :
Chromium minimum 11.5 %
Excellent corrosion resistance
The addition of nickel gives good toughness & strength at sub-zero and elevated temperatures
Welding: Loose corrosion resistance on exposure over 500 deg. C
No, preheat and fast cooling
Low current & stringer beads
Tool Steels:
Used as Cutting Tools, Shear Blades, Dies, etc.
Contain high carbon
Have a high amount of tungsten, molybdenum, chromium, cobalt, etc., and withstand temperatures up to 550 deg.
Welding: Difficult to weld.
High preheat around 350 deg. C & cool slowly
Hence, we at Ador Fontech have designed & developed this exclusive range of LH low heat input welding electrodes, TIG rods & MIG wires to weld all types of steel used in industry, resolving all problems as the unique solution provider for maintenance & repair welding.
To join ferrous with non-ferrous metals, various methods can be adopted.
Mechanical methods: Fasteners, rivets, etc.
Adhesive bonding method: Brazing and Soldering (a.k.a. welding)
Base metal does not fuse: Molten filler gets drawn into close-fit joints through capillary action (surface tension forces).
Brazing filler melts at >450⁰C, soldering at <450⁰C
Welding is the most commonly used process of all.
Welding – A Definition
Welding can be described as a process of joining two or more pieces /edges of metal by producing a localized union through heat (fusion) with or without pressure to create a homogenous joint.
Types of Welding by Metal:
Autogenous: In this process, similar materials are joined without filler wire or electrode Heterogeneous: Process of joining dissimilar materials, using a filler wire or welding electrode
Metal Inert Gas welding or Metal Active Gas welding
SAW – Submerged Arc Welding
2. Solid-State and other Non-electric Fusion Welding: Examples of non-fusion, non-electric process welding are:-
Thermit welding
Ultrasonic welding
Diffusion welding
Deformation welding.
Welding Processes
Fusion welding: Welding in the liquid state with no pressure, Union is by molten metal bridging
Solid State welding: Carried out below the melting point of the metal without filler additions, Pressure is often used,
Union is often by plastic flow.
Solid State welding:
DEFORMATION WELDING: Two Surfaces in contact are brought into very close contact by applying high pressure, which deforms them. E.g., – Forge welding, Roll welding, Extrusion welding. (Not at very high temperatures)
DIFFUSION WELDING: Joining takes place by atomic diffusion of 2 surfaces in contact. Surfaces are usually heated to high temperatures (below the melting point) & pressure may be employed. E.g., Brazing, Braze welding & Soldering. Soldering is an oxy-fuel process of joining metals. The process temperature does not exceed 450⁰. Brazing is also an Oxy-Fuel joining process. The process temperature is between 450⁰ Degrees – 750⁰ degrees. Braze welding is similar to Brazing; the process temperature is above 750⁰ Degrees but below the melting point of the base metal.
Non-Fusion Process: Thermit welding is the most common process used in joining of railway tracks. In this process iron powders and Al binders are kept in Vat or a conical container above the joining rails. When they are fired due to chemical reaction and exothermic reaction, the iron powder melts and forms a joint between rails.
Introduction to Arc Welding: Basic welding processes used in Industry are
MMAW – Manual Metal Arc Welding or Shielded Metal Arc welding
GMAW – Gas Metal Arc Welding/ Flux Cored Arc Welding (MIG, MAG)
GTAW – Gas Tungsten Arc Welding (TIG)
SAW – Submerged Arc Welding
MMAW or SMAW- Shielded Metal Arc process: In the Shielded Metal Arc process or Manual metal Arc welding process the arc is established between Parent Metal and a flux coated welding electrode using electrical energy to melt and deposit weld metal. This is the most commonly used process in the world.
Basic Requirements for the SMAW process:
Heat source: Welding Equipment Current Range 30-400 A –depending on size of the electrode in general, even though there are welding machines used up to 600 Amps AC or DC welding machines can be used in SMAW Operation.
Welding Consumable: Flux coated welding electrode (1.6- 8 mm diameter)
A trained welder is required to operate the process, So SMAW or MMAW is the most commonly used process in the world.
SMAW Process advantages:
This is the simplest of all welding process.
Equipment Portable
Economical Cost of Equipment
Variety of application & wide availability of electrodes
Range of metals & their alloys can be welded
Welding in all Positions
Welding in Indoor & Outdoors
Extended welding cable to long distances in comparison to another process
Limitations of SMAW process:
Low productivity as in a 10-minute cycle welding happens only for 6 minutes
Process also involves a frequent changes of welding electrode
Moisture from flux coatings can create weld-related problems
Safety problems like arc strike, Stray current & electric shock risks
Absolutely Manual process – hence called Manual metal arc welding
GMAW & FCAW processes:
A continuous solid wire, small diameter
GMAW uses solid wire, no flux
FCAW use flux-filled wire
Wire feed through the gun to the arc by wire feeder.
Weld pool may be protected from oxidation by shielding gas.
High productivity 3 kg/h or more
Direct current (DCEP mostly).
Process Requirement:
Welding power source
Wire feeder mechanism- In-built/separate
Gun with gas supply & trigger switch
1. Manual/semi-automatic guns
2. Automatic torches available
3. Can be fitted to automation etc.
Advantages in GMAW:
Faster as compared to TIG & SMAW.
Can produce joints with deep penetration.
Thick & thin, jobs can be welded effectively.
Can be used for fabrication and maintenance repair job.
Can be mechanized easily
Reduced distortion.
Limitation in GMAW:
More Complex due to
Electrode stick-out
Torch angle
Welding parameters
Type and size of electrode
Welding torch manipulation
Not suitable for outdoor welding applications
GTAW or TIG welding: GTAW or Tungsten Inert gas welding uses a consumable Tungsten electrode as the heat source.
This consists of the below. Heat source – welding power source to create an arc between a tungsten tip and the parent metal
30-400A, AC or DC welding machine and 0-20V
Inert gas shielding is used in the process. Consumable: filler rod can be used between 1 to 4mm diameter Process Features:
Excellent control
1. Stable arc at low power (80A at 11V)
2. Independently added filler
3. Ideal for intricate welds eg root runs in the pipe or thin sheet
4. Low productivity 0.5kg/h manual
High quality
1. Clean process, no slag
2. Low oxygen and nitrogen weld metal
3. Defect-free, excellent profile even for single-sided welds
Advantages in GTAW/TIG Process:
No slag inclusion
Clear visibility of arc and job
All position weldability
Suitable for high quality welding of thin material
Root run of thick materials
Ideal for Aluminum, Stainless steel & Titanium
Limitations in GTAW:
Slow as compared to SMAW/MIG/MAG & SAW welding
Possibility of tungsten inclusion in the weld deposit which is hard & brittle
Not suitable for outdoor welding
Submerged Arc welding process (SAW Process): In the Saw Process, as the name signifies, welding happens submerged beneath the flux. SAW process also employs welding consumables usually a wire & arc is established between the welding wire and base metal and welding happens underneath the metal powder of flux, shielding the arc from the atmosphere and its gases.
Heat source: Arc between a wire and base metal Current Range: 200 Amps -1200 Amps
DC operation Power Consumption
35-56 KVA
Power source
Welding head and control box
Welding head travel
Flux recovery system (optional)
Positioners and Fixtures
Hence the basic difference between the two processes is that in the SMAW process, the flux-coated electrode provides the shielding from the atmosphere & in SAW process an external flux is delivered at the arcing area to act as a shield, so welding happens underneath the powder flux fed by a delivery system.
SMAW Process – Advantages:
Simplest of all Arc welding process
Equipment is portable
Economical cost of equipment
Variety of application & wide availability of electrodes
Range of metals & their alloys can be welded
Welding in all Positions
Welding in Indoor & Outdoors
Extended welding cable to long distances when compared to other processes
SAW Process advantages:
High productivity up to 2 to 10 kg per hour
Speed almost up to 2m/ min
Can be easily automated for even higher productivity
Limitations of the SAW process:
Bulky, expensive, and heavy equipment
Flat and horizontal positions only
Thicker sections (6mm and above)
Mostly ferrous materials (also Ni alloys)
Conclusion: A wide variety of processes are available for joining or hard surfacing ferrous and non-ferrous materials. Each of these processes provides different mechanical properties and works in specific conditions, with a welding power source. There are several factors to consider in welding rod selection:
Base metal properties
Tensile strength required
Welding current
Base metal thickness, shape and joint fit-up
Welding position
Specification and service conditions
No. of similar jobs – Scope for automation
Environmental job conditions
These methods are all commonly used by Industry. Before we select any particular method for welding, we need to analyze each of the factors listed above.
ADFL serves the industry with the manufacture and supply of all types of consumables for MMAW, MIG /Mag, TIG, SAW & non-fusion processes like soldering, brazing, and braze welding. This is why Ador Fontech’s name is synonymous with total solutions for any maintenance & repair problem, ensuring the Life Enhancement of Industrial components, to the complete satisfaction of customers.
It also contains Silicon- 0.5%-3%, Manganese-0.2%-1.3%, Phosphorous-0.8% max & Sulphur -0.2%max. The major distinguishing feature between steels is carbon content, it has maximum influence on the property of CI. A low percentage promotes the formation of hard white cast iron & higher percentage promotes the formation of grey cast iron.
